This invention relates to a cool keeping transportable arrangement and also to a method to assist in keeping cool materials for transport purposes.
The problem to which this invention is addressed relates to the difficulties associated with keeping materials, typically biological materials, within a selected cool range of temperatures during transport.
Pharmaceutical and similar companies have need to transport quantities of biological materials including blood products, vaccines and some prescription lines that must be kept cool in transport but which cannot be allowed to freeze. Such materials are sometimes accompanied by an instruction to store at a low temperature, typically four degrees Centigrade. Generally, these products are based on water which therefore contains some dissolved materials (e.g. normal saline, 0.9% sodium chloride). Such materials therefore have a freezing point a little below zero degrees Centigrade.
Transport of retail quantities of these products has increasingly relied on insulated containers containing a coolant block to maintain temperatures in the range 0 to 8 degrees Centigrade for the period of transport. Arbitrary test schemes have been established by large companies and health authorities to ensure reliability of the coolant systems to deliver the products in good condition. The existing coolant systems rely on the establishment of a steadystate temperature within the required range whereby the rate at which heat is absorbed by the coolant equals the rate at which heat enters the cold area via the insulation. To prevent freezing of the product at low ambient temperatures, the coolants are frozen at a relatively high temperature, typically minus six degrees Centigrade, or are allowed to stand for a time above zero degrees Centigrade prior to use. These procedures limit the useful life of the coolant, and provide no guarantee that the products will not freeze.
It is preferable that standard deep freeze equipment can be utilized to freeze and store coolant systems and it is an object of the present invention to provide a package which can thus utilize standard deep freeze equipment and yet maintain the temperature of stored product above freezing.
There is proposed in accordance with the invention a storage container for storage of temperature sensitive materials during transport, the storage container being characterized in that it includes:
an outer layer or container of coolant material able to be frozen to temperatures substantially below the freezing point of water,
a removable inner separating layer configured to separate the material to be stored and transported from the outer layer, or container, the inner separating layer containing a volume of water therein, the volume of water being determined in proportion to the amount and temperature of the coolant material in the outer layer
Preferably, the relative proportions of water in the inner separating layer and the outer layer are selected such that during typical transport times the temperature of material held in the container is maintained within the temperature range 0-8xc2x0 C.
Using the outer layer and the separating layer as described the container or package of the present invention takes advantage of the physical properties of ice and water mixtures.
A mixture of ice and water at atmospheric pressure defines zero degrees. At this temperature there is equilibrium between ice and water. Attempts to heat the mixture does not alter the temperature but simply causes ice to melt at a rate of one gram of ice melting per 334 joules of heat energy absorbed, that is the heat of fusion of ice. When all ice has melted, the water temperature can then rise. The opposite is true on cooling down ice water mixture. Water at zero degrees Centigrade will form ice on releasing heat. This process can be driven by having material present at a lower temperature which can absorb the heat and drive the process. Thus, in the present case the outer layer of coolant material can be frozen and stored using standard deep freeze equipment. A separating layer can be maintained in a cold space such as a refrigerator or cold room at a temperature above zero degrees Centigrade in a non-frozen state.
When it is necessary to transport temperature sensitive material the outer layer and separating layer can be combined so that the separating layer is in contact with the material and holds the temperature of the material above zero degrees Centigrade.
The quantity of water necessary in the separating product can be calculated from a consideration of the temperature of the outer layer bearing in mind the specific heat of ice at that temperature and also the latent heat of fusion of ice.
Typically the outer layer would be deep frozen to xe2x88x9230 degrees Centigrade in commercially available deep freeze units. The specific heat of ice at xe2x88x9230 degrees Centigrade is approximately 1.88 joules per gram per degree Centigrade. The specific heat of ice at zero degree Centigrade is 2.1 joules per gram per degree Centigrade. The outer layer may be, for example, a vaccine box.
Thus, 100 grams of ice frozen to xe2x88x9230 Centigrade can absorb approximately 5971 joules of heat from water at 0 degrees Centigrade.
In turn, to form ice at 0 degrees Centigrade from water at 0 degrees Centigrade requires 334 joules per gram. Accordingly 5971/334=17.9 grams of ice could be produced. Therefore, provided the separating layer contains at least 18 grams of water per 100 grams of deep frozen ice product, the separating layer can prevent freezing of the temperature sensitive products it contains during normal transport times and ambient temperatures, .
In preference, the separating layer comprises a liquid contained within a holding package. In some forms of the invention, the water in the inner separating layer may be in gelled or other supported forms.
In preference, the separating layer comprises water held within one or more bags or pockets and such that the shape of such a bag or pocket is either appropriate that the material can be placed so as to be surrounded by the liquid held in the bag or bags or that the bag or bags can be rolled or folded appropriately to surround any smaller biological material.
One of the problems with an arrangement such as this is that if the separating material is not consistently located so as to ensure that it will always provide a separation between a frozen material and the sample, then there is a possibility that direct contact of the frozen material, perhaps through only thin sheets of plastics separation, can freeze some part or all of the sample.
In preference then, there is a continuous bag to hold the separating layer and within the bag, a spreader which will retain the ice water mixture therethrough and keep this substantially spread throughout the full area of the pocket or pockets.
It is appreciated that the quantity of separating layer has to be sufficient so that, given a time over which coolness within a selected temperature range is to be achieved, that such materials both in terms of quantities and in terms of initial temperatures and in terms of ambient temperature situations, will ensure an adequate result.
In preference, the separating layer is kept at an initial stage in a storage means so that the temperature is at a temperature that is appropriate for the longer storage of the biological material so that the two parts can be kept in a cold storage prior to transport together.
In preference then, if there is a small sample of biological material to be kept within the temperature from 0 degree Centigrade to 6 degrees Centigrade, both a surrounding package of water and the sample would be kept within the refrigerator at a temperature of say 5 degrees Centigrade.
When the biological material is called for to be transported to a different place and needs to be kept over a sustained period within the temperature range, the combination of separating layer with the biological material embedded in this, is inserted in a cool keeping container where now, a frozen material held within an insulating outer, can be at a substantially lower temperature than otherwise would hitherto have been available.
In a typical example which will be described in the embodiments, such outer frozen materials can now be started at a temperature of say minus 22 degrees Centigrade knowing that the biological material will be kept from any freezing temperature by the intervening material containing water surrounding the biological material.
In experiments conducted thus far, very substantial extensions of time have been achieved with relatively economic and efficient packaging using these concepts.